1. Field of the Invention
The present invention relates to a coating process method and a coating process apparatus, in which a substrate such as a semiconductor wafer is coated with a liquid coating material such as a resist.
2. Description of the Related Art
In the manufacturing process of a semiconductor device, a resist pattern that is used as a mask for forming a prescribed pattern is formed by means of a so-called “photolithography technology”, in which a resist solution is supplied onto a semiconductor wafer so as to form a resist film, followed by applying a light exposure treatment in a prescribed pattern to the wafer after the resist coating step and subsequently developing the light-exposed pattern formed on the resist film on the wafer. In the resist coating process among the manufacturing steps noted above, a spin coating method is employed in many cases as a method for uniformly coating the wafer surface with the resist solution.
In the spin coating method, a resist solution is dripped from a resist nozzle arranged above the wafer W onto the central portion of the wafer surface while rotating the wafer W together with a spin chuck by a rotary driving mechanism, with the wafer W held stationary on the spin chuck by means of vacuum suction. The dripped resist solution is centrifugally expanded radially outward on the wafer surface so as to form a resist film on the entire surface of the wafer W. Then, the dripping of the resist solution is stopped, and the rotation of the wafer W is continued so as centrifugally remove the extra resist solution on the wafer surface, thereby controlling the thickness of the resist film and drying the resist film.
In order to form a resist pattern with a high precision, it is necessary to form the resist film in a prescribed uniform thickness over the entire surface of the wafer W. Also, for forming the resist film in a uniform thickness over the entire surface of the wafer W, it is important to control strictly the resist solution dripping time, and the timing of the resist solution dripping and the wafer rotation in addition to the rotating speed and the rotating time of the wafer W.
It was customary in the past to supervise the thickness and the thickness distribution of the resist film by controlling the coating device, etc. with a software.
However, in the conventional resist solution supply mechanism, resist discharging nozzles of a plurality of resist coating process units are connected to a single resist solution discharging pump, with the result that, because of the installing conditions such as the difference in head, the discharging timing of the resist solution tends to be rendered nonuniform depending on the resist solution discharging nozzle used even if the resist solution is discharged on the basis of the same recipe. The discharging timing of the resist solution is also rendered nonuniform by the individual variation of the air operation valve used as an opening-closing valve of the resist solution supply pipe or the resist solution discharging pump. Such a nonuniformity in the discharging time was not handled as a serious problem in the past. However, a prominent progress is being achieved in recent years in the miniaturization of the semiconductor device and in the enlargement in the diameter of the semiconductor substrate to be process. In this connection, very high levels of the demands for the accuracy in the thickness of the resist film and for the uniformity of the resist film thickness are being raised nowadays. It follows that even the nonuniformity in the discharging timing of the resist solution caused by the difference in head and by the individual variation has come to affect seriously the thickness and the uniformity of the thickness of the resist film. It should also be noted that the reduction in the discharging amount of the resist solution (resist saving) is being promoted in recent years so as to affect the change in the discharging amount and the change in the discharging rate of the resist solution.